1. Field of the Invention
The present invention relates to a method of manufacturing an electrode for a fuel cell.
2. Description of Prior Art
There is widely known a fuel cell as a power generating system instead of a thermal power generation system. An electrochemical cell such as a fuel cell is constituted by a number of plied electrodes and accordingly, when any one of the electrodes becomes faulty, there causes an trouble of the cell as a whole. Accordingly, it is necessary to employ a large-scale production system for electrodes having good quality for the fuel cells.
FIG. 1 is a cross-sectional view showing a construction of the electrodes in a phosphoric acid fuel cell using carbon papers as an electrode substrate. For clarification, an air electrode 1 and a fuel electrode 2 are shown in a disassembled state in FIG. 1. The air electrode 1 is constituted by a carbon paper 3 having a thickness of ranging from 300 .mu.m to 600 .mu.m, a catalytic layer 4 having a thickness of ranging from about 50 .mu.m to about 200 .mu.m and a packing 5 made of fluorine-containing rubber. The fuel electrode 2 is constituted by a carbon paper 3 same as that of the air electrode 1, a catalytic layer 8 having a thickness of ranging from about 30 .mu.m to about 150 .mu.m, a wet-sealing part 6, a peripheral gas-sealing part 7 and a matrix layer 9 having a thickness of about 150 .mu.m. The matrix layer 9 is formed integrally with the fuel electrode in the figure (although it may be formed as an independent layer) and therefore, the matrix layer 9 is considered as a part of the fuel electrode.
FIG. 2 is a cross-sectional view showing a construction of a phosphoric acid fuel cell using ribbed electrodes in which a numeral 10 designates as a whole a ribbed electrode. There are generally two types of electrodes for fuel cells inclusive of a phosphoric acid type fuel cell and the other types of fuel cells.
Heretofore, there have been proposed various methods to manufacture the electrodes. A spraying method have been generally used as the most simple way. Namely, the spraying method comprises coating a solution including a fairly small amount of solid content on substrates which constitute the peripheral sealing layer 7, the catalytic layers 4, 8 and the matrix layer 9 and drying the solution, the step being repeated several times until the thickness of dried solid content reaches a predetermined level. However, the spraying method has the disadvantage that many steps are required and a large amount of paste is wasted and accordingly it is difficult to carry out a large-scale production and therefore not economical.
A screen-printing method has also been utilized. However, it requires many steps of hand operations and it is difficult to utilize the method for production of a large-sized electrode suitable for practical use and the method is not suitable for a large-scale production.
A drying method has been utilized to form the catalytic layers 4, 8 shown in FIG. 2. However, a large amount of paste has been wasted and therefore, the drying method is uneconomical as is the spraying method. Particularly, an phosphoric acid fuel cell requires relatively large amount of platinum for the electrode. Accordingly, an amount of paste to be used should be minimized as much as possible.
Thus, the conventional methods are uneconomical and are not suitable for a large-scale production. Further, in either conventional method, it is necessary to form the catalytic layers 4, 8 and the peripheral sealing layer 7 separately which inevitably requires many steps. Accordingly, a method for economical and large-scale production with an automation system is desired to manufacture an electrode for a phosphoric acid fuel cell which is expected to be in use in the near feature.
The inventors have studied to use at first a doctor blade method; however, it has been found that use of a reverse roll coating method is advantageous from the viewpoint of easy control of the thickness of layers.